Secondary batteries are in widespread use for powering electronic devices such as cell-phones and IT devices, not to mention replacing primary batteries. In particular, because nonaqueous electrolyte secondary batteries represented by lithium ion batteries have high energy density, application of them to industrial large electric devices such as electric cars is facilitated.
The nonaqueous electrolyte secondary battery includes a metallic container as a housing container, in general. Because the metallic container has electric conductivity, a short circuit may accidentally occur through the metallic container during use of the battery. Therefore, for the purpose of preventing the short circuit, covering of the metallic housing container with an insulating film is practiced widely and conventionally (see JP-A-2011-175942 (FIG. 14), for example).
The nonaqueous electrolyte secondary battery in the related art described above has the following problems. In many cases, as the insulating film, a cylindrical heat shrinkable tube is applied as disclosed in JP-A-2011-175942 and the tube is put over the housing container of the battery and heated and shrunk to complete the covering. However, it is difficult to obtain the finished covering which exactly conforms to a shape of the metallic container. Moreover, such inexact covering has insufficiently shrunk parts. If the battery is exposed to a thermally severe environment, e.g., if the battery is left for a long period of time or used continuously in a hot place, the parts may shrink again and come off covered portions and, as a result, a surface of the housing container may be exposed.
As described above, in the conventional electric storage device including the nonaqueous electrolyte secondary battery, it is difficult to accurately and properly put insulating covering conforming to the shape of the housing container.